Reduction of nitro compounds



Patented Oct. 4, 1927.

UNITED STATES I Latent? PATENT OFFHCE.

RALPH A. NnLso AND ANTON PRASIL, or serum, NEW YORK, ASSIGNORS T0 NATIONAL ANILINE & CHEMICAL COMPANY, INC., on NEW Yoax,'N. Y., A COR- PORATION OF NEW YORK.

REDUCTION OF NITRO COMPOUNDS.

No Drawing.

This invention relates to improvements in the reduction of nitro compounds, and more particularly to thG-IGdllCtlOIl of nitro compounds to hydrazo compounds, by means of Zinc and caustic alkali as the reducing agents. The invention also relates to provements in the separation and isolation of the hydrazo compounds, at the end of the reduction. The invention includes improvements in the reduction operation, in the extraction and isolation operation, and 1n the combined reduction'and isolation operations; 7

The present invention is-based upon the discovery that the reduction of nitro compounds to hydrazo compounds by means of zinc and caustic alkali can be carried out with advantage withthe aid of an organlc solvent immiscible with water, such as benzene, toluene, etc., so that there is directly produced, as the result of the reduction, :1 solution of the hydrazo compounds 1n the immiscible solvent in admixture with the zinc residue. By carrying out the reduction in this way the disadvantages and objections resulting from the reduction as heretofore carried out are overcome or very greatly reduced, so that the hydrazo compounds can be produced with good yield. I

In the preferred practice of the invention, the nitro compound in solution in benzene or other solvent, is subjected to reduction by means of zinc and caustic alkali, and the zinc and caustic alkali are intermittently added, and the reaction is controlled by the regulated addition of these reducing agents.

In its broader aspects, the invention includes the carrying out of the reduction with zinc and caustic alkali, regardless of the manner in which they are added, but it is particularly advantageous, in order to secure effective control of the reaction, to add the zinc and caustic both intermittently and progressively so that any considerable accumulation of the reagents is avoided, with the avoidance of the possibility of their suddenly taking hold and causing the reaction to roceed with explosive violence. The gradua l and intermittent addition of the zinc and caustic also makes possible the regulation of the reduction in such a Way that it may be stopped at theazoxy or azo point of the solvent.

'of a larger amount of by-products.

Application filed June 22, 1920. Serial-No. 390,885..

presence of excess water are thus avoided, as well as difficulties due to the separation of crystals in admixture with the zinc resi due. However, it should be borne in mind that it is essential to have a small amount of water present in order that a complete reduction ma be effected.

It is a further characteristic of the invention that the reduction can be carried out at a relatively low temperature, particularly when benzene or toluene are used as" a solvent, since, by using a reflux and carrying out the reaction under refluxing conditions the working temperature of the reduction is substantially that of the boiling Higher boiling solvents can also be used, if the temperature 1s so controlled that it does not exceed the low temperatures at which but little byproducts are formed. The higher temperatures of'higher boiling solvents are in general undesirable as they favor the formation The best solvent is benzene, owing to its low boiling-point which allows an easy control for carrying out the reduction at a low temperature, and also to its increased solvent action upon the hydrazo compounds.

At the end of the reduction, the hydrazo compound is contained in solution in the hot solvent and, this solution is in admixture with the zinc residue. By driving off the solvent, the zinc residue and the hydrazo compound can be directly obtained in admixture, but it is more advantageous to separate the solution of the hydrazo compound from the zinc residue. If the amount of solvent used is not sufficient for complete extraction of the hydrazo compound a further amount of solvent can be added suflicient'for the complete solution and extrac-' tion, or the extraction can be carried out in stages by separatingthe solution present at the end of the reduction and subsequently adding further amounts of the solvent to complete the extraction. Owing to the absence of any substantial amount of water, the'zinc residue is in a form well adapted for the se aration therefrom of. the solution and for the extraction of the hydrazo compound in case it is not entirely in solution.

lVhere the same solvent is used durin the reduction of the nitro compounds to by razo compounds and for the separationjof the hydrazo compounds from the zinc residue, there is avoided the added operation incident to the use of a different solvent. for the reduction and extraction, and the solution of hydrazo compound can be directly produced at the end'of the reduction. This solution of hydrazo compound can be readily separated from the zmc residue and the hydrazo obtained in an isolated state free from zinc, while the zinc residue itself can likewise be obtained substantially free from organic matter, and directly available vfor use without calcination or further treatment, for special purposes.

It will thus be seen that the process of the present invention, in its entirety, involves the reduction of the nitro compound in the presence of the'immiscible solvent, and the extraction and recovery of the hydrazo compound from the zinc residue by the immiscible solvent, thus obtaining in a simple and advantageous manner a solution of the hydrazo compound in a state of-high purity and with excellent yield, while leaving the zinc residue in an isolated state. It will also be seen that the various steps of the process, as well as the fprocess in its entirety, present features 0 novelty and of advantage.

The invention will be further illustrated by the following specific examples, the parts being by weight:

- Reduction of o-nitmm'sol.

150 parts of o-nitranisol and 220 parts of benzene are charged into a suitable receptacle and brought to a boil under refluxing conditions; that is, with the use of a reflux condenser. The mixture is vigorously agitated and the reduction of the o-nitranisol is effected by the addition of zinc and caustic soda, making use of about 45 parts of caustic soda of 35 to 40 B. and about 200 parts of zinc dust. The zinc dust and caustic soda are advantageously added intermittently, adding one or the other at such a rate as to keep up a vigorous reflux action. The progress of the reaction canthus be regulated, and any large excess of either the zinc or caustic can be avoided, whileinsuring that. sufiicient of both are present for the continuation of the reaction at the appropriate rate, or as fast as is permitted by the reflux action. The completlon of the reduction may require several hours, and will vary with the amount'of material treated,

\with therate of addition, and with other and the azo stages, and finally to the hydrazo stage.

At the end of the reduction, the'benzene solution of hydrazanisol can be separated from the zinc residue and the zinc residue then extracted and washed with further amounts of benzene, or further amounts of benzene can be added directly to the reduction product, and substantially the entire amount of hydrazanisol extracted at once from the zinc residue. The residue can then be washed one or more times to complete the extraction of soluble matter therefrom, and the washed liquors so obtained can beused in the further carrying out of the process, by dissolving in them the further amounts of nitro compound to be reduced; The zinc residue can be freed from the adhearing solvent b distillation and can thus be obtained in a ried and isolated state, Well adapted for special purposes without incineration or further treatment.

The benzene solution of hydrazanisol produced aseabove described, can be directly used for the conversion of the hydrazanisol to dianisidine; for example, in the manner described in the companion applications SerialNos. 390,886 and 390,887, filed June 22, 1920. The hydrazanisol can also be separated from the benzene solution, for

Reduction of nitrobenzene.

150 parts of nitro-benzene and 200 parts of benzene are mixed together in a suitable receptacle and heated to refluxing condition with a reflux condenser. The mixture is vlgorously agitated and the nitro-benzene is then reduced to the hydrazobenzene by means of zinc and caustic soda using about 32 parts of caustic soda of 35 to 40 1313., and

about 200 parts of zinc dust. The zinc dust and caustic soda are added intermittently and in small portions, adding one\ or the other as needed at such a rate as to'keep up a vigorous refluxing action. When all the zinc and caustic have been added, the heatresidue washed with further amounts of. benzene and the last traces of benzene removed from the zin residue by distillation. The hydrazobenzene is thus obtained in solution, and the solution itself may be used, for example, for rearrangement of the hydrazobeuzcne to benzidine or the hydrazobenzene can itself be separated from the solution by crystallization or by dlstillation .oi the benzene.

In a similarnianner o-nitrotoluene can be reduced tohydrazotoluene and the hydrazotoluene obtained either in an isolated state, or directly in the form of a solution well adapted for treatment for the'rearrangement of the hydrazotoluene to tolidine.

In the process above described it will be noted that the amount of caustic soda used is only a small fraction of the amount theoretically required to convert the zinc into zincate. In Example 1, the amount of caustic soda used is about 6.4% to' 7.9% of the weight of zinc used, or about 5.25% to (3.387 of the theoretical amount necessary to convert the zinc into sodium zincate. In Example 2, the amount of caustic soda is about 4.6% to 5.5% of the weight of the zinc used. or about 3.75% to 4.53% of the amount theoretically required to convert the zinc into zincate. It will thus be seen that the amount of caustic soda may vary from about 3.5% to 7% of the amount theoretically required to convert the zinc present into sodium zincate, and that zinc to the extentof more than about twelve (12) times that required to form sodium zincate with the caustic soda will be present at the end of the reduction, mainly as zinc oxide .or hydrated oxide, with the presence of only a. very small amount of sodium zincate This materially facilitates the separation of the solution of hydrazo compound and results in giving a zinc oxide product directly usable for special purposes.

It is to be understood that the water of the caustic soda solution is a requisite in the process, since it furnishes the necessary hydrogen over and above the amount of hydrogen furnished by the relatively small amount of caustic soda used. In the course of the reaction of the zinc and caustic soda, while it is not definitely known, it seems that the zinc passes through the sodium zincate stage in producing the zinc oxide found in the zinc residue. Another theory is that the sodium zincate acts as a catalyst in the reaction.

The ma'or portion of the reduction appears to be e ected by the reaction between zinc and water, thereaction taking place in the presence of caustic-soda. 4

In the claimsthe words a few percent"? are to be construed broadly to embrace the limits4.5% to 8%, referring to the weight of zinc used as previously set forth.

We claim: i

1. The method of reducing a nitro compound, which comprises subjecting the nitro compound, in solution in an organic solvent immiscible with water, to the reducing action of zinc and caustic alkali, the amount of zinc being in excess of that required to form sodium zlncate with the caustic alkali.

2. The method of reducing a nitro compound to a hydrazo compound, which comprises subjecting the nitro compound, in solution in an organic solvent immiscible with water, to the reducing action of zinc and caustic alkali until the hydrazo stage is reached, the amount of zinc being in excess of that required to form sodium zincate with the caustic alkali.

3. The method of reducing o-nitranisol to hydra-zanisol, which comprises subjecting the o-nitranisolto the reducing action of zinc and caustic alkali in the presence of an organic solvent immiscible with water, the amount of zinc being in' excess of that required to form sodium zincate with the caustic alkali.

a. The method of producing and isolating a hyrazo compound, which comprises subjecting 9. nitro compound to reduction with zinc and caustic alkali in the presence of an organic solvent immiscible with water and thereby producing directly a solution of hydrazo compound in the or anic solvent, and separating such solution rom the zinc residue, the amount of zinc present being in excess of that required to form sodium zincate with the caustic alkali.

5. The method of roducing and isolating a hydrazo compoun which comprises subjecting a nitro compound to reduction with zinc and caustic'alkali in the presence of an organic solvent immiscible with water, add mg further amounts of the solvent-at the end of the reduction, and separating the solution of hydrazo compound from the zinc residue, the amount of zinc being in excess of that'- required to form sodium zincate with the caustic alkali. i

6. The method of reducing a nitro compound which comprises subjecting the nitro compound in solution in a solvent of the benzene series having a low boiling point to the reducing action of zinc and caustic alkali at about the boiling temperature of said solvent, the amount of zinc present being more about twelve times that required to form sodium zincate with the caustic alkali. 7. The method of reducing a nitro combenzene series havin 'poundto a hydrazo compound which comprises subjectin the nltro compound in solution in a so vent of the benzene series having a low boiling point to the reducing action of zinc and caustic alkali at approximately the boiling point of the solvent until the hydrazo stage is reached, the amount of zinc present being more than about tyvelve times that required to form sodium iincate with the caustic alkali.

pound, which comprises subjecting the nitro compound in benzene solution to the action of zinc in the presence of aqueous caustic alkali, the amount of caustic alkali being only a few' percent of the amount required to convert the zinc into zincate."

10. The method of producing hydrazanisol, which comprises subjecting about 150 parts of o-nitranisol and 220 parts of henzene to the action of about .45 parts of caustic soda of 36- to 40 B. and about 200 parts of zinc dust at the boiling point of the benzene, separating the benzene from the hydrazo compound ormed, and treatin the zinc residue with further amounts 0 benzene until soluble admixtures are removed, thereby leaving the zinc residue substantially free from soluble admixtures.

11. The method of producing hydrazanisol, which comprises subjecting about 150 parts of o-nitranisol and 220 parts of benzene to the action of about 45 parts of canstic soda of 35' to 40 B. and about 200 parts of zinc dust at the boiling point of the benzene, the zinc and caustic soda being added intermittently in small portions, separating the benzene from the hydrazo compound formed, and treatin the zinc residue with further amounts 0 benzene until solubleadmixtures are removed, thereby leaving the zinc residue substantially free from soluble admixtures.

12. A process for the reduction of a nitro compound of the aromatic series, which comprises acting on the nitro compound with zinc and caustic alkali in the presence of an organic solvent immiscible with water, the amount of caustic alkali being only a few percent of the amount required to convert the zinc into zincate.

13. A process for the reduction of onitranisol to roduce hydrazanisol, which comprises acting on the o-nitranisol with zinc and caustic alkali in the present of a liquid organic solvent immiscible with Water, the amount of caustic alkali being only a few percent of the amount required to convert to zinc into zincate.

14. The method of reducing a mono-nitro compound, which comprises subjecting the mono-nitro compound, in solution in an organic solvent immiscible with water, to the reducing action of zinc and caustic alkali, the amount of zinc being in excess of that required to form sodium zincate. with the caustic alkali.

15. A process for reducing a mono-nitro compound of the benzene ser1es, which comprises subjecting the nitro compound in the presence of an organic solvent immisci ble with water to the action of zinc and a solution of caustic alkali containing an amount of caustic alkali of about 3.5 to 7 per cent of the amount required to convert the zinc into zincate.

16. A process for reducing a mono-nitro compound of the benzene series, which coulprises subjecting the nitro compound in the presence of a low boiling hydrocarbon of the benzene series to the action of zinc and a solution of caustic alkali in'water containing an amount of caustic alkali of about 3.5 to 7 percent of the amount required to convert the zinc into zincate.

17. A process for the reduction of a mono-nitro compound of the benzene series,

which comprises subjecting the nitro compound, in the presence of an organic solvent immiscible with water, to the action of zinc and a solution of caustic alkali in water containing an amount of caustic alkali of about 3.5 to 7 percent of the amount required to convert the zinc into zincate, the zinc being added to the rest of the ingredients in small portions intermittently. v

18. A process for the reduction of o-nitranisol to hydranzanisol, which comprises subjecting the o-nitranisol, in the presence of boiling benzene, to the action of zinc and a solution of caustic alkali, the amount ofv caustic alkali being about 3.5 to 7 percent of the amount required to convert the zinc into zincate.

19. A process for the reduction of o-nitranisol to hydrazanisol, which comprises subjecting the o-nitranisol, in the presence of boilingbenzene, to the action of zinc and a solution of caustic alkali in water containing an amount of caustic alkali of about 3.5 to 7 percent of the amount required to convert zinc into zincate, the zinc being added to the rest of the ingredients in smallportions intermittently.

In testimony whereof we aflix tures.

our signa- RALPH. A. NELSON. ANTON PRASIL. 

